1. Field of the Invention
The present invention relates to a camera system which incorporates a seamless lens-drive switching mechanism with which lens drive mode can be switched between power lens drive mode, in which a movable lens group can be driven by motor, and manual lens drive mode, in which the same movable lens group can be driven manually.
2. Description of the Related Art
Among conventional lens barrels having either an automatically or manually adjustable focus, a lens barrel which is provided with the following elements is known in the art: a stationary ring, a movable ring which supports a focusing lens group and is arranged concentrically with the stationary ring to be movable forward and rearward in an optical axis direction, a distance adjustment ring which is arranged concentrically with the stationary ring and moves the movable ring forward and rearward in the optical axis direction by rotating about the axis of the distance adjustment ring, an AF driving force transfer mechanism which receives a driving force for rotating the distance adjustment ring from a motor installed in a camera body, and a manual focus ring (manual operation ring) which is manually rotated about the axis thereof to rotate the distance adjustment ring.
This type of lens barrel is disclosed in Japanese Unexamined Patent Publication Nos. H02-253214 and H02-253210.
However, in the lens barrel disclosed Japanese Unexamined Patent Publication No. H02-253214, the manual focus ring inevitably rotates when an auto-focusing operation is performed because a driving force of the motor is transferred to the manual focus ring when an auto-focusing operation is performed. Therefore, if the hand of the user comes in contact with the manual focus ring during the auto-focusing operation, the auto-focusing operation cannot be performed smoothly.
In the lens barrel disclosed in Japanese Unexamined Patent Publication No. H02-253210, although the manual focus ring does not rotate even if a driving force of the motor is transferred to the manual focus ring when an auto-focusing operation is performed, the manual focus ring cannot be easily rotated manually (an MF (manual focus) operation cannot be easily performed) because a predetermined load is always applied to the manual focus ring to prevent the manual focus ring from rotating easily.